Traffic signals are widely used throughout the world to control the flow of vehicular and foot traffic on and across roadways. Most commonly, traffic signals include one or more lighted sections, whose shape, relative location and/or color conveys commands or prohibitions to motorists and/or pedestrians. Perhaps the most common example is the three colored traffic signal, featuring three distinct round lights, or round groups of lights, in red, yellow and green. When the lights are arranged vertically, the red light is usually on top with the yellow and green lights thereunder, in that order. When the lights are arranged horizontally, the red light is usually to the left, with the yellow and green lights to the right thereof, in that order. A very common pedestrian traffic signal features the words DON'T WALK or STOP and WALK or GO, or alternatively pictograms representing standing and walking people, in alternate sections.
While these conventional traffic signals have the advantage of being very widely recognized and understood, they convey relatively little information to the pedestrian or motorist. Some improvements have been advanced to allow additional information to be conveyed by traffic signals; for instance, the inclusion of a graphical or numerical countdown at pedestrian crosswalks. However, further improvements are still possible.